5alpha-reduced androgens may have actions in the hippocampus to enhance cognitive performance of male rats

The association of caffeine and nandrolone decanoate modulates aversive memory and nociception in rats

Caffeine and anabolic-androgenic steroids (AAS) are commonly used to improve muscle mass and athletic performance. Nandrolone Decanoate (ND) is one of the most abused AAS worldwide, leading to behavioral changes in both humans and rodents. Caffeine, the most widely consumed psychostimulant globally, is present in various thermogenic and gym supplements. Low and moderate doses of caffeine antagonize adenosine receptors and have been linked to improved memory and pain relief. We have previously demonstrated that consuming caffeine prevents the risk-taking behavior triggered by nandrolone. In this study, we aimed to investigate the long-term effects of ND and caffeine, either alone or in combination, on passive avoidance memory and nociception. We used the step-down and hot-plate tasks in male and female Lister Hooded rats. Our results confirmed the antinociceptive effect of caffeine and indicated that chronic administration of the ND-caffeine association promotes the evocation of aversive memory in female rats.

Spatial working memory in a disappearing object task is impaired in female but not male dogs with chronic osteoarthritis

Chronic pain in humans is associated with impaired working memory but it is not known whether this is the case in long-lived companion animals, such as dogs, who are especially vulnerable to developing age-related chronic pain conditions. Pain-related impairment of cognitive function could have detrimental effects on an animal's ability to engage with its owners and environment or to respond to training or novel situations, which may in turn affect its quality of life. This study compared the performance of 20 dogs with chronic pain from osteoarthritis and 21 healthy control dogs in a disappearing object task of spatial working memory. Female neutered osteoarthritic dogs, but not male neutered osteoarthritic dogs, were found to have lower predicted probabilities of successfully performing the task compared to control dogs of the same sex. In addition, as memory retention interval in the task increased, osteoarthritic dogs showed a steeper decline in working memory performance than control dogs. This suggests that the effects of osteoarthritis, and potentially other pain-related conditions, on cognitive function are more clearly revealed in tasks that present a greater cognitive load. Our finding that chronic pain from osteoarthritis may be associated with impaired working memory in dogs parallels results from studies of human chronic pain disorders. That female dogs may be particularly prone to these effects warrants further investigation.

It is all About the Chase: Neurosteroidogenesis in Male Rats is Driven by Control of Mating Pace

BACKGROUND

Masculine sexual behaviors are dependent on androstane-derived steroids; however, the modulatory effects of mating, and of mating control, on androstane neurosteroidogenesis remain largely unknown.

OBJECTIVE

Herein, we investigated the effects of mating control, prior sexual experience, and age on brain region specific neurosteroidogenic responses in male rats.

METHODS

Effects of acute sexual experience were tested in naïve male rats that either remained sexually- naïve, were exposed to a standard mating chamber, or were either given control of the mating pace in a standard mating chamber (male control) or mated wherein the female stimulus rat controlled the mating pace in a paced-mating chamber (female control). Aged (10-12 months) sexually responsive male rats were similarly euthanized from the homecage or engaged in male controlled or female controlled mating. All rats were euthanized immediately following exposure conditions for radioimmunoassay of steroids in midbrain, hypothalamus, hippocampus and cortex.

RESULTS

Consummatory sexual behavior in male vs. female-controlled mating paradigms was altered by age and prior sexual experience. Male-controlled mating increased androstane neurosteroid metabolism, such that complementary increases in the testosterone (T) metabolite 5α-androstane-3α-17β- diol (3α-diol) in the midbrain and hypothalamus of male rats corresponded to decreases in the prohormone, T. 3α-diol were increased in the hippocampus in response to the context alone, and to a lesser degree in response to mating. Mating diminished neurosteroidogenesis in the cortex. Neurosteroidogenesis was overall reduced in aged male rats compared to naïve controls, however, these effects were more prominent in sexually non-responsive aged male rats.

CONCLUSION

Extending previous findings, these results indicate differential production of androstane neurosteroids in a mating exposure, age and brain region dependent manner.

Testosterone protects mice against zika virus infection and suppresses the inflammatory response in the brain

Testosterone is essential to human growth and development as well as immune regulation. Zika virus (ZIKV), an emerging arbovirus associated with neurological complications including neuroinflammation, can also cause testicular damage and decrease testosterone secretion. However, whether the dysregulation of testosterone plays a role in the process of neuroinflammation during ZIKV pathogenesis is still unclear. In this study, we found that ZIKV infection caused testicular damage and decreased testosterone secretion in male mice, and testosterone supplementation after ZIKV infection reduced their mortality and attenuated the pathological symptoms. Further investigation revealed that testosterone treatment after ZIKV infection alleviated inflammation and nerve injury in the mouse brain. Additionally, reduced CD8⁺ T cell infiltration and interferon-gamma production were observed in brains of testosterone-treated mice. Overall, our results demonstrated that testosterone plays a protective role in ZIKV-infected mice, and thus it can be developed as a potential therapeutic drug against ZIKV infection.

Intact Female Mice Acquire Trace Eyeblink Conditioning Faster than Male and Ovariectomized Female Mice

Female subjects have been widely excluded from past neuroscience work because of a number of biases, including the notion that cycling sex hormones increase variability. However, it is necessary to conduct behavioral research in mice that includes both sexes as mice are typically used for developing and evaluating future therapeutics. Understanding sex differences in learning is fundamental for the development of targeted therapies for numerous neurologic and neurodegenerative disorders, including Alzheimer’s disease, which is more prevalent in females than males. This study set out to confirm the role of sex and necessity of circulating ovarian hormones in the acquisition of the temporal associative memory task trace eyeblink conditioning (tEBC) in C57BL/6J mice. We present evidence that sex and ovarian hormones are important factors in learning. Specifically, intact female mice learn significantly faster than both male and ovariectomized (ovx) female mice. Data from pseudoconditioned control mice indicate that sex differences are because of differences in learned associations, not sensitization or spontaneous blink rate. This study strengthens the idea that ovarian hormones such as estrogen and progesterone significantly influence learning and memory and that further research is needed to determine the underlying mechanisms behind their effects. Overall, our findings emphasize the necessity of including both sexes in future behavioral studies.

Androgen Affects the Inhibitory Avoidance Memory by Primarily Acting on Androgen Receptor in the Brain in Adolescent Male Rats

Adolescence is the critical postnatal stage for the action of androgen in multiple brain regions. Androgens can regulate the learning/memory functions in the brain. It is known that the inhibitory avoidance test can evaluate emotional memory and is believed to be dependent largely on the amygdala and hippocampus. However, the effects of androgen on inhibitory avoidance memory have never been reported in adolescent male rats. In the present study, the effects of androgen on inhibitory avoidance memory and on androgen receptor (AR)-immunoreactivity in the amygdala and hippocampus were studied using behavioral analysis, Western blotting and immunohistochemistry in sham-operated, orchiectomized, orchiectomized + testosterone or orchiectomized + dihydrotestosterone-administered male adolescent rats. Orchiectomized rats showed significantly reduced time spent in the illuminated box after 30 min (test 1) or 24 h (test 2) of electrical foot-shock (training) and reduced AR-immunoreactivity in amygdala/hippocampal cornu Ammonis (CA1) in comparison to those in sham-operated rats. Treatment of orchiectomized rats with either non-aromatizable dihydrotestosterone or aromatizable testosterone were successfully reinstated these effects. Application of flutamide (AR-antagonist) in intact adolescent rats exhibited identical changes to those in orchiectomized rats. These suggest that androgens enhance the inhibitory avoidance memory plausibly by binding with AR in the amygdala and hippocampus.

Regulation of risky decision making by gonadal hormones in males and females

Psychiatric diseases characterized by dysregulated risky decision making are differentially represented in males and females. The factors that govern such sex differences, however, remain poorly understood. Using a task in which rats make discrete trial choices between a small, "safe" food reward and a large food reward accompanied by varying probabilities of footshock punishment, we recently showed that females are more risk averse than males. The objective of the current experiments was to test the extent to which these sex differences in risky decision making are mediated by gonadal hormones. Male and female rats were trained in the risky decision-making task, followed by ovariectomy (OVX), orchiectomy (ORX), or sham surgery. Rats were then retested in the task, under both baseline conditions and following administration of estradiol and/or testosterone. OVX increased choice of the large, risky reward (increased risky choice), an effect that was attenuated by estradiol administration. In contrast, ORX decreased risky choice, but testosterone administration was without effect in either ORX or sham males. Estradiol, however, decreased risky choice in both groups of males. Importantly, none of the effects of hormonal manipulation on risky choice were due to altered shock sensitivity or food motivation. These data show that gonadal hormones are required for maintaining sex-typical profiles of risk-taking behavior in both males and females, and that estradiol is sufficient to promote risk aversion in both sexes. The findings provide novel information about the mechanisms supporting sex differences in risk taking and may prove useful in understanding sex differences in the prevalence of psychiatric diseases associated with altered risk taking.

Involvement of Testosterone Signaling in the Integrity of the Neurovascular Unit in the Male: Review of Evidence, Contradictions, and Hypothesis

Age-related central nervous system function decline and increased susceptibility of females compared to males with respect to prevalence of several neurodegenerative and neuropsychiatric diseases are both based on the principle that hormonal factors could be involved. These cerebral disorders are characterized by an alteration of blood-brain barrier (BBB) properties and chronic neuroinflammation, which lead to disease progression. Neuroinflammation, in turn, contributes to BBB dysfunction. The BBB and its environment, called the neurovascular unit (NVU), are crucial for cerebral homeostasis and neuronal function. Interestingly, sex steroids influence BBB properties and modulate neuroinflammatory responses. To date however, the majority of work reported has focused on the effects of estrogens on BBB function and neuroinflammation in female mammals. In contrast, the effects of testosterone signaling on the NVU in males are still poorly studied. The aim of this review was to summarize and discuss the literature, providing insights and contradictions to highlight hypothesis and the need for further investigations.

Advances in Knowledge of Androgens: How Intentional and Accidental Neurosteroid Changes Inform Us of Their Action and Role

Purpose of Review

Here, we summarize current knowledge of androgens’ action gained over the recent years.

Recent Findings

Neurosteroids are produced in the brain and peripheral nerves, independent of endocrine glands have been investigated for how they are regulated, and have actions via non-steroid receptor targets to mediate social, affective, and cognitive behavior and to protect the brain. Androgens’ organizing actions in the peri-natal period have effects throughout the lifetime that may be recapitulated later in life during critical periods and at times of challenge. Developmental changes in androgens occur during mid-childhood, adrenarche, puberty, adolescence, young adulthood, middle age, and andropause. Changes in androgens with a 5α-reductase inhibitor, such as finasteride, result in disruptions in organizational and activational functions of androgens that can be unremitting.

Summary

Normal developmental or perturbation in androgens through other means can cause changes in androgen-sensitive phenotypes throughout the lifespan, in part through actions of neurosteroids.

Changes in Hippocampal Androgen Receptor Density and Behavior in Sprague-Dawley Male Rats Exposed to a Low-Pressure Blast Wave

Objective

The purpose of this study was to examine the effect of exposure of a low-intensity blast wave on androgen receptor (AR) density in the hippocampus and the potential influence on behavioral and cognitive responses.

Methods

Sprague-Dawley rats were randomly assigned to either a blast exposed group (n = 27) or an unexposed (control) group (n = 10). Animals were treated identically, except that rats within the control group were not exposed to any of the characteristics of the blast wave. Behavior measures were conducted on day seven post-exposure. The rats were initially assessed in the elevated plus maze followed by the acoustic startle response paradigm. Spatial memory performance using the Morris water-maze test was assessed at 8-days post-exposure, for seven consecutive days. Following all behavioral tests AR immunofluorescence staining was performed in different hippocampal subregions.

Results

A significant elevation in anxiety index (p < 0.001) and impaired learning (p < 0.015) and spatial memory (p < 0.0015) were noted in exposed rats. In addition, a significant attenuation of the AR was noted in the CA1 (p = 0.006) and dentate gyrus (p = 0.031) subregions of the hippocampus in blast exposed animals. Correlational analyses revealed significant associations between AR and both anxiety index (r = -.36, p = 0.031) and memory (r = -0.38, p = 0.019).

Conclusions

The results of this study demonstrate that exposure to a low-pressure blast wave resulted in a decrease in AR density, which was associated with significant behavioral and cognitive changes.

Learning and the Lifespan: What's Sex Got to Do With It?

Engagement in sexual behavior can impact neurosteroidogenesis, in particular production of the prohormone testosterone (T) and likely its subsequent metabolism to 5α-androstane-3α-17β-Diol (3α-Diol) or aromatization to estradiol (E₂). Androgens and their metabolites vary across the lifespan and impact many behaviors, including cognition, anxiety, and sexual behavior. Thus, we hypothesized that mating may alter cognitive performance via androstane neurosteroids in an age- and experience-dependent manner. We first investigated if exposure to mating during memory consolidation could enhance performance in the novel object recognition task (NOR). Male rats were trained in NOR and then immediately exposed to mating-relevant or control stimuli. Following a 4 h inter-trial interval (ITI), male rats were tested for object memory. Male rats that were exposed to a receptive female during the ITI had better performance in NOR. We then investigated if these effects were due to novelty associated with mating. Male rats were exposed to mating-relevant stimuli and identified as sexually responsive (SR) or sexually non-responsive (SNR) based on a median split of engagement in mating with the stimulus female. We found that a brief history (10 min session daily for five consecutive days) of sexual history substantially influenced performance in the NOR task, such that SR males had better performance in the NOR task, but only when presented with the opportunity to mate during the ITI. As T levels substantially decrease with age in male rodents, we investigated whether the effects of long-term sexual experience (10 months) influenced neurosteroids and NOR performance in mid-aged (12 months old) males. Mid-aged SR males maintain neural T; however, they have decreased neural E₂ and decreased cognitive performance at 12 months compared to mid-aged SNR rats. In sexually experienced rats, those with better cognitive performance had greater levels of T metabolites (e.g., 3α-Diol in mated SR males, E₂ in mid-aged SNR rats). While naïve males that were mated during the ITI had better cognitive performance, T metabolites were decreased compared to controls. These findings suggest that T metabolites, but not the prohormone, may influence learning dependent on sexual proclivity, experience, and proximate opportunity to mate.

Testosterone and Adult Neurogenesis

It is now well established that neurogenesis occurs throughout adulthood in select brain regions, but the functional significance of adult neurogenesis remains unclear. There is considerable evidence that steroid hormones modulate various stages of adult neurogenesis, and this review provides a focused summary of the effects of testosterone on adult neurogenesis. Initial evidence came from field studies with birds and wild rodent populations. Subsequent experiments with laboratory rodents have tested the effects of testosterone and its steroid metabolites upon adult neurogenesis, as well as the functional consequences of induced changes in neurogenesis. These experiments have provided clear evidence that testosterone increases adult neurogenesis within the dentate gyrus region of the hippocampus through an androgen-dependent pathway. Most evidence indicates that androgens selectively enhance the survival of newly generated neurons, while having little effect on cell proliferation. Whether this is a result of androgens acting directly on receptors of new neurons remains unclear, and indirect routes involving brain-derived neurotrophic factor (BDNF) and glucocorticoids may be involved. In vitro experiments suggest that testosterone has broad-ranging neuroprotective effects, which will be briefly reviewed. A better understanding of the effects of testosterone upon adult neurogenesis could shed light on neurological diseases that show sex differences.

Combined dipeptidyl peptidase-4 inhibitor with low-dose testosterone exerts greater efficacy than monotherapy on improving brain function in orchiectomized obese rats

Both obesity and orchiectomy lead to the development of brain pathologies and cognitive decline. Testosterone replacement therapy (2 mg/kg/day TRT) and dipeptidyl peptidase-4 inhibitor (vildagliptin) improved cognition in orchiectomized rats, and obese rats. However, both had no beneficial effects in brain of orchiectomized-obese rats. TRT (>2 mg/kg/day) is possible to attenuate brain defects in those rats, but high dose of TRT causes adverse effects. Then, combined effect of low-dose TRT (1 mg/kg/day) and vildagliptin on brain and cognitive functions in orchiectomized-obese rats should be investigated. Sixty male rats were fed with either a normal diet (ND) or a high-fat diet (HFD) for 28 weeks. At week 13, both ND and HFD-fed rats had either a sham-operation or an orchiectomy. At week 25, orchiectomized rats were treated with either: a vehicle, 2 mg/kg/day TRT, vildagliptin (3 mg/kg/day) or a combined vildagliptin with 1 mg/kg/day TRT for 4 weeks. Then, metabolic parameters, brain and cognitive functions were determined. Hippocampal oxidative stress, apoptosis, dendritic spine loss, microglial hyperactivity, and cognitive decline were found in orchiectomized ND-fed rats and sham-operated HFD-fed rats. Interestingly, orchiectomy aggravated these brain pathologies and cognitive decline in HFD-fed rats. In orchiectomized ND-fed rats, all treatments restored brain and cognitive functions. In orchiectomized HFD-fed rats, monotherapies ameliorated these brain pathologies, while the combined therapies had the greatest beneficial effect on the brains. These findings suggest the combined therapies may be the best therapeutic approach for restoring brain functions in the orchiectomized-obese condition.

Impairment of learning and memory performances induced by BPA: Evidences from the literature of a MoA mediated through an ED

Many rodent studies and a few non-human primate data report impairments of spatial and non-spatial memory induced by exposure to bisphenol A (BPA), which are associated with neural modifications, particularly in processes involved in synaptic plasticity. BPA-induced alterations involve disruption of the estrogenic pathway as established by reversal of BPA-induced effects with estrogenic receptor antagonist or by interference of BPA with administered estradiol in ovariectomized animals. Sex differences in hormonal impregnation during critical periods of development and their influence on maturation of learning and memory processes may explain the sexual dimorphism observed in BPA-induced effects in some studies. Altogether, these data highly support the plausibility that alteration of learning and memory and synaptic plasticity by BPA is essentially mediated by disturbance of the estrogenic pathways. As memory function in humans involves similar signaling pathways, this mode of action of BPA has the potential to alter human cognitive abilities.

5alpha-reductase inhibitors dampen L-DOPA-induced dyskinesia via normalization of dopamine D1-receptor signaling pathway and D1-D3 receptor interaction

Although 1-3,4-dihydroxyphenylalanine (L-DOPA) is the mainstay therapy for treating Parkinson's disease (PD), its long-term administration is accompanied by the development of motor complications, particularly L-DOPA induced dyskinesia (LID), that dramatically affects patients' quality of life. LID has consistently been related to an excessive dopamine receptor transmission, particularly at the down-stream signaling of the striatal D₁ receptors (D₁R), resulting in an exaggerated stimulation of cAMP-dependent protein kinase and extracellular signal-regulated kinase (ERK) pathway. We previously reported that pharmacological blockade of 5alpha-reductase (5AR), the rate-limiting enzyme in neurosteroids synthesis, attenuates the severity of a broad set of behavioral alterations induced by D₁R and D₃R activation, without inducing extrapyramidal symptoms. In line with this evidence, in a recent study, we found that inhibition of 5AR by finasteride (FIN) produced a significant reduction of dyskinesia induced by L-DOPA and direct dopaminergic agonists in 6-OHDA-lesioned rats. In the attempt to further investigate the effect of 5AR inhibitors on dyskinesia and shed light on the mechanism of action, in the present study we compared the effect of FIN and dutasteride (DUTA), a potent dual 5AR inhibitor, on the development of LID, on the therapeutic efficacy of L-DOPA, on the molecular alterations downstream to the D₁R, as well as on D₁R-D₃R interaction. The results indicated that both FIN and DUTA administration significantly reduced development and expression of LID; however, DUTA appeared more effective than FIN at a lower dose and produced its antidyskinetic effect without impacting the ability of L-DOPA to increase motor activation, or ameliorate forelimb use in parkinsonian rats. Moreover, this study demonstrates for the first time that 5AR inhibitors are able to prevent key events in the appearance of dyskinesia, such as L-DOPA-induced upregulation of striatal D₁R-related cAMP/PKA/ERK signaling pathways and D₁R-D₃R coimmunoprecipitation, an index of heteromer formation. These findings are relevant as they confirm the 5AR enzyme as a potential therapeutic target for treatment of dyskinesia in PD, suggesting the first ever evidence that neurosteroidogenesis may affect functional interaction between dopamine D₁R and D₃R.

Sex hormones and the development of sexual size dimorphism: 5α-dihydrotestosterone inhibits growth in a female-larger lizard (Sceloporus undulatus)

Sexual differences in adult body size [sexual size dimorphism (SSD)] and color (sexual dichromatism) are widespread, and both male- and female-biased dimorphisms are observed even among closely related species. A growing body of evidence indicates testosterone can regulate growth, thus the development of SSD, and sexual dichromatism. However, the mechanism(s) underlying these effects are conjectural, including possible conversions of testosterone to estradiol (E₂) or 5α-dihydrotestosterone (DHT). In the present study, we hypothesized that the effects of testosterone are physiological responses mediated by androgen receptors, and we tested two specific predictions: (1) that DHT would mimic the effects of testosterone by inhibiting growth and enhancing coloration, and (2) that removal of endogenous testosterone via surgical castration would stimulate growth. We also hypothesized that females share downstream regulatory networks with males and predicted that females and males would respond similarly to DHT. We conducted experiments on eastern fence lizards (Sceloporus undulatus), a female-larger species with striking sexual dichromatism. We implanted Silastic^® tubules containing 150 µg DHT into intact females and intact and castrated males. We measured linear growth rates and quantified color for ventral and dorsal surfaces. We found that DHT decreased growth rate and enhanced male-typical coloration in both males and females. We also found that, given adequate time, castration alone is sufficient to stimulate growth rate in males. The results presented here suggest that: (1) the effects of testosterone on growth and coloration are mediated by androgen receptors without requiring aromatization of testosterone into E₂, and (2) females possess the androgen-receptor-mediated regulatory networks required for initiating male-typical inhibition of growth and enhanced coloration in response to androgens.

Stress and adolescent hippocampal neurogenesis: diet and exercise as cognitive modulators

Adolescence is a critical period for brain maturation. Deciphering how disturbances to the central nervous system at this time affect structure, function and behavioural outputs is important to better understand any long-lasting effects. Hippocampal neurogenesis occurs during development and continues throughout life. In adulthood, integration of these new cells into the hippocampus is important for emotional behaviour, cognitive function and neural plasticity. During the adolescent period, maturation of the hippocampus and heightened levels of hippocampal neurogenesis are observed, making alterations to neurogenesis at this time particularly consequential. As stress negatively affects hippocampal neurogenesis, and adolescence is a particularly stressful time of life, it is important to investigate the impact of stressor exposure at this time on hippocampal neurogenesis and cognitive function. Adolescence may represent not only a time for which stress can have long-lasting effects, but is also a critical period during which interventions, such as exercise and diet, could ameliorate stress-induced changes to hippocampal function. In addition, intervention at this time may also promote life-long behavioural changes that would aid in fostering increased hippocampal neurogenesis and cognitive function. This review addresses both the acute and long-term stress-induced alterations to hippocampal neurogenesis and cognition during the adolescent period, as well as changes to the stress response and pubertal hormones at this time which may result in differential effects than are observed in adulthood. We hypothesise that adolescence may represent an optimal time for healthy lifestyle changes to have a positive and long-lasting impact on hippocampal neurogenesis, and to protect against stress-induced deficits. We conclude that future research into the mechanisms underlying the susceptibility of the adolescent hippocampus to stress, exercise and diet and the consequent effect on cognition may provide insight into why adolescence may be a vital period for correct conditioning of future hippocampal function.

Neural Androgen Receptor Deletion Impairs the Temporal Processing of Objects and Hippocampal CA1-Dependent Mechanisms

We studied the role of testosterone, mediated by the androgen receptor (AR), in modulating temporal order memory for visual objects. For this purpose, we used male mice lacking AR specifically in the nervous system. Control and mutant males were gonadectomized at adulthood and supplemented with equivalent amounts of testosterone in order to normalize their hormonal levels. We found that neural AR deletion selectively impaired the processing of temporal information for visual objects, without affecting classical object recognition or anxiety-like behavior and circulating corticosterone levels, which remained similar to those in control males. Thus, mutant males were unable to discriminate between the most recently seen object and previously seen objects, whereas their control littermates showed more interest in exploring previously seen objects. Because the hippocampal CA1 area has been associated with temporal memory for visual objects, we investigated whether neural AR deletion altered the functionality of this region. Electrophysiological analysis showed that neural AR deletion affected basal glutamate synaptic transmission and decreased the magnitude of N-methyl-D-aspartate receptor (NMDAR) activation and high-frequency stimulation-induced long-term potentiation. The impairment of NMDAR function was not due to changes in protein levels of receptor. These results provide the first evidence for the modulation of temporal processing of information for visual objects by androgens, via AR activation, possibly through regulation of NMDAR signaling in the CA1 area in male mice.

Gonadectomy reduces the density of androgen receptor-immunoreactive neurons in male rat's hippocampus: testosterone replacement compensates it

BACKGROUND

In the present study, the role of gonadectomy on memory impairment and the density of androgen receptor-immunoreactive neurons in rats' hippocampus as well as the ability of testosterone to compensate of memory and the density of androgen receptors in the hippocampus was evaluated.

METHODS

Adult male rats (except intact-no testosterone group) were bilaterally castrated, and behavioral tests performed 2 weeks later. Animals bilaterally cannulated into lateral ventricles and then received testosterone (10, 40 and 120 µg/0.5 µl DMSO) or vehicle (DMSO; 0.5 µl) for gonadectomized-vehicle group, 30 min before training in water maze test. The androgen receptor-immunoreactive neurons were detected by immunohistochemical technique in the hippocampal areas.

RESULTS

In the gonadectomized male rats, a memory deficit was found in Morris water maze test on test day (5th day) after DMSO administration. Gonadectomy decreased density of androgen receptor-immunoreactive neurons in the rats' hippocampus. The treatment with testosterone daily for 5 days attenuated memory deficits induced by gonadectomy. Testosterone also significantly increased the density of androgen receptor-immunoreactive neurons in the hippocampal areas. The intermediate dose of this hormone (40 µg) appeared to have a significant effect on spatial memory and the density of androgen receptor-immunoreactive neurons in gonadectomized rats' hippocampus.

CONCLUSIONS

The present study suggests that testosterone can compensate memory failure in gonadectomized rats. Also testosterone replacement can compensate the reduction of androgen receptor-immunoreactive neurons density in the rats' hippocampus after gonadectomy.

Effects of testosterone on synaptic plasticity mediated by androgen receptors in male SAMP8 mice

Synaptic changes are closely associated with cognitive deficits. In addition, testosterone (T) is known to exert regulative effects on synaptic plasticity. T may improve cognitive deficits in Alzheimer's disease (AD) patients, but the underlying mechanisms of androgenic action on cognitive performance remain unclear. The aim of this study was thus to examine the protective mechanism attributed to T on cognitive performance in an AD senescence, accelerated mouse prone 8 (SAMP8) animal model. Using Golgi staining to quantify the dendritic spine density in hippocampal CA1 region, molecular biomarkers of synapse function were analyzed using immunohistochemistry and western blot. T significantly increased the dendritic spine density in hippocampal CA1 region, while flutamide (F) inhibited these T-mediated effects. Immunohistochemistry and western blot analysis showed that the expression levels of brain derived neurotrophic factor (BDNF), postsynaptic density 95 (PSD-95), and p-cyclic-AMP response element binding protein (CREB)/CREB levels were significantly elevated in the T group, but F reduced the T-induced effects in these biomarkers to control levels. There were no significant differences in the expression levels of PSD-95, BDNF, and p-CREB/CREB between C and F. These findings indicate that the effects of T on improvement in synaptic plasticity were mediated via androgen receptor (AR). It is conceivable that new treatments targeted toward preventing synaptic pathology in AD may involve the use of androgen-acting drugs.

Effects of Testosterone Treatment on Synaptic Plasticity and Behavior in Senescence Accelerated Mice

Learning and memory are known to be influenced by circulating sex steroidal hormones and these behavioral processes are diminished in aging. Thus, the aim of this study was to examine the mechanism underlying testosterone-induced effects on cognitive performance in the senescence accelerated mouse P8 (SAMP8) model. Treatment with testosterone (T) as evidenced by the Morris water maze test produced a significantly shorter escape latency and reduced path length to reach the platform compared to the control (C). No significant differences were noted in mean swim speed among all groups. During the probe trials, the T group spent a significantly greater percent of time in the target quadrant and improved the number of platform crossings. Flutamide (F), an antiandrogen, significantly inhibited the effects of T on behavioral and memory performances indicators. Following Nissl staining, the number of intact pyramidal cells was markedly elevated in the treated mice, and this effect was blocked by F. Immunohistochemistry and Western blot analysis showed that the expression levels of NMDAR1, SYN, and p-CREC/CREB protein levels were significantly increased in the T group, while F inhibited the T-mediated effects. Western blot analysis showed that there were no significant differences in the expression levels of SYN, p-CREC/CREB, and NMDAR1 between C, F, and F + T groups. Reverse-transcription polymerase chain reaction (RT-PCR) analysis showed that the mRNA expression levels of NMDAR1 and SYN were significantly increased in T-administered mice, while F inhibited the T-mediated effects. Data suggest that the T-mediated increase in SYN expression levels resulted in improvement in behavioral performances and learning, which may involve stimulation of central nervous system androgen receptors (AR).

The value of middle phalangeal hair as an anthropometric marker: A review of the literature

Middle phalangeal hair (MPH) is a trait frequently examined in anthropological studies throughout the 20th century. MPH is found on the back of the middle segment of the fingers, excluding the thumb. Typically, researchers examined the presence and absence of hair in various populations, and described it in terms of age, ancestry, and sex. Recently MPH has been examined as a potential anthropometric indicator of: androgen levels, androgen-related side effects in women, gene homozygosity, and disease resistance. Given the potential value of this marker, the present paper provides a comprehensive overview of MPH and its associated characteristics (i.e., ethnicity, sex, age, and hormonal variations) and presents new data on the reliability of MPH assessment. Findings suggest that ethnicity, sex, and age need to be controlled in any studies examining MPH and its relationship with other variables. Two measures of MPH (i.e., presence/absence of MPH and actual hair count) are both acceptable to use in MPH assessment; and the use of a hand lens to examine MPH provides high reliability when MPH is assessed by expert raters. However, researchers should avoid participant self-assessment. Future avenues for research are suggested (e.g., measurement issues and studies on hormonal correlates in women). MPH could be useful in research or for clinical purposes as a possible non-invasive indicator of hormone levels or hormonal sensitivity, or of predisposition toward androgen-related or gene-homozygosity-related health issues or behaviors.

3α-diol administration decreases hippocampal PKA (II) mRNA expression and impairs Morris water maze performance in adult male rats

The effect of testosterone and its metabolites on learning and memory has been the subject of many studies. This study used the Morris water maze task to investigate the effect of intra-hippocampal injection of 3α-diol (one of the metabolites of testosterone) on acquisition stage of spatial memory in adult male rats. During the experiment we observed that 3α-diol, significantly impaired Morris water maze performance in treated rat's compared with controls. Because signaling event mediated by protein kinase A (PKA) especially PKA (II) are critical for many neuronal functions such as learning and memory, the hippocampus was analyzed for mRNA expression of PKA (II) using TaqMan real time RT-PCR. The results indicated that the transcription levels of PKA (II) were significantly decreased in animals treated with 3α-diol compared with controls. Thus, the findings suggest that administration of 3α-diol in hippocampus of adult male rats impairs memory function, possibly via down-regulation of PKA.

Amelioratory effects of testosterone treatment on cognitive performance deficits induced by soluble Aβ1-42 oligomers injected into the hippocampus

This study was undertaken to investigate the protective effects and potential mechanism of testosterone (T) on cognitive performance in adult male rats given bilateral intrahippocampal injections of beta amyloid 1-42 oligomers (Aβ1-42) combined with gonadectomy (Aβ+GDX). A series of experiments were designed to verify the optimal administration time and dose of T and to explore its potential protective mechanisms on spatial ability in Aβ+GDX rats in the Morris water maze test. Aβ1-42 was injected only once two weeks before testing, while T and the androgen receptor (AR) antagonist flutamide (F) were administered daily beginning 2 days before and throughout the 6 days of testing. The Aβ1-42 injection and GDX individually impaired cognitive performance, and the combination of these treatments was additive, leading to even greater impairment. The serum T level peaked at 48 h after administration. T doses ranging from 0.25 to 1.00 mg corresponding to serum T levels of 4.5-21.35 ng/ml improved the spatial ability. Animals administered 0.75 mg of T corresponding to the serum T level of 15.2 ng/ml had the most significantly improved behavioral performances. However, higher T doses of 1.50 and 2.00 mg resulting in serum T levels of 34.8 and 45 ng/ml, respectively, impaired the behavioral performances. F had no effect on the serum T level and spatial ability, but it blocked the activational effect of T. These findings indicate that the effect of T on behavioral performances is partly mediated through ARs.

Testosterone depletion in adult male rats increases mossy fiber transmission, LTP, and sprouting in area CA3 of hippocampus

Androgens have dramatic effects on neuronal structure and function in hippocampus. However, androgen depletion does not always lead to hippocampal impairment. To address this apparent paradox, we evaluated the hippocampus of adult male rats after gonadectomy (Gdx) or sham surgery. Surprisingly, Gdx rats showed increased synaptic transmission and long-term potentiation of the mossy fiber (MF) pathway. Gdx rats also exhibited increased excitability and MF sprouting. We then addressed the possible underlying mechanisms and found that Gdx induced a long-lasting upregulation of MF BDNF immunoreactivity. Antagonism of Trk receptors, which bind neurotrophins, such as BDNF, reversed the increase in MF transmission, excitability, and long-term potentiation in Gdx rats, but there were no effects of Trk antagonism in sham controls. To determine which androgens were responsible, the effects of testosterone metabolites DHT and 5α-androstane-3α,17β-diol were examined. Exposure of slices to 50 nm DHT decreased the effects of Gdx on MF transmission, but 50 nm 5α-androstane-3α,17β-diol had no effect. Remarkably, there was no effect of DHT in control males. The data suggest that a Trk- and androgen receptor-sensitive form of MF transmission and synaptic plasticity emerges after Gdx. We suggest that androgens may normally be important in area CA3 to prevent hyperexcitability and aberrant axon outgrowth but limit MF synaptic transmission and some forms of plasticity. The results also suggest a potential explanation for the maintenance of hippocampal-dependent cognitive function after androgen depletion: a reduction in androgens may lead to compensatory upregulation of MF transmission and plasticity.

Therapeutic testosterone administration preserves excitatory synaptic transmission in the hippocampus during autoimmune demyelinating disease

Over 50% of multiple sclerosis (MS) patients experience cognitive deficits, and hippocampal-dependent memory impairment has been reported in >30% of these patients. While postmortem pathology studies and in vivo magnetic resonance imaging demonstrate that the hippocampus is targeted in MS, the neuropathology underlying hippocampal dysfunction remains unknown. Furthermore, there are no treatments available to date to effectively prevent neurodegeneration and associated cognitive dysfunction in MS. We have recently demonstrated that the hippocampus is also targeted in experimental autoimmune encephalomyelitis (EAE), the most widely used animal model of MS. The objective of this study was to assess whether a candidate treatment (testosterone) could prevent hippocampal synaptic dysfunction and underlying pathology when administered in either a preventative or a therapeutic (postdisease induction) manner. Electrophysiological studies revealed impairments in basal excitatory synaptic transmission that involved both AMPA receptor-mediated changes in synaptic currents, and faster decay rates of NMDA receptor-mediated currents in mice with EAE. Neuropathology revealed atrophy of the pyramidal and dendritic layers of hippocampal CA1, decreased presynaptic (Synapsin-1) and postsynaptic (postsynaptic density 95; PSD-95) staining, diffuse demyelination, and microglial activation. Testosterone treatment administered either before or after disease induction restores excitatory synaptic transmission as well as presynaptic and postsynaptic protein levels within the hippocampus. Furthermore, cross-modality correlations demonstrate that fluctuations in EPSPs are significantly correlated to changes in postsynaptic protein levels and suggest that PSD-95 is a neuropathological substrate to impaired synaptic transmission in the hippocampus during EAE. This is the first report demonstrating that testosterone is a viable therapeutic treatment option that can restore both hippocampal function and disease-associated pathology that occur during autoimmune disease.

Dissociating behavioral, autonomic, and neuroendocrine effects of androgen steroids in animal models

Developments in behavioral assessment, autonomic and/or baseline reactivity, psychopharmacology, and genetics, have contributed significantly to the assessment of performance-enhancing drugs in animal models. Particular classes of steroid hormones: androgenic steroids are of interest. Anecdotally, the performance enhancing effects of androgens are attributed to anabolic events. However, there is a discrepancy between anecdotal evidence and investigative data. While some androgen steroids may promote muscle growth (myogenesis), effects of androgens on performance enhancement are not always seen. Indeed, some effects of androgens on performance may be attributable to their psychological and cardiovascular effects. As such, we consider androgen effects in terms of their behavioral, autonomic, and neuroendocrine components. Techniques are discussed in this chapter, some of which are well established, while others have been more recently developed to study androgen action. Androgens may be considered for their positive impact, negative consequence, or psychotropic properties. Thus, this review aims to elucidate some of the effects and/or mechanisms of androgens on behavioral, autonomic, and/or neuroendocrine assessment that may underlie their controversial performance enhancing effects.

The role of testicular hormones and luteinizing hormone in spatial memory in adult male rats

Attempts to determine the influence of testicular hormones on learning and memory in males have yielded contradictory results. The present studies examined whether testicular hormones are important for maximal levels of spatial memory in young adult male rats. To minimize any effect of stress, we used the Object Location Task which is a spatial working memory task that does not involve food or water deprivation or aversive stimuli for motivation. In Experiment 1 sham gonadectomized male rats demonstrated robust spatial memory, but gonadectomized males showed diminished spatial memory. In Experiment 2 subcutaneous testosterone (T) capsules restored spatial memory performance in gonadectomized male rats, while rats with blank capsules demonstrated compromised spatial memory. In Experiment 3, gonadectomized male rats implanted with blank capsules again showed compromised spatial memory, while those with T, dihydrotestosterone (DHT), or estradiol (E) capsules demonstrated robust spatial memory, indicating that T's effects may be mediated by its conversion to E or to DHT. Gonadectomized male rats injected with Antide, a gonadotropin-releasing hormone receptor antagonist which lowers luteinizing hormone levels, also demonstrated spatial memory, comparable to that shown by T-, E-, or DHT-treated males. These data indicate that testicular androgens are important for maximal levels of spatial working memory in male rats, that testosterone may be converted to E and/or DHT to exert its effects, and that some of the effects of these steroid hormones may occur via negative feedback effects on LH.

Effect of 3α-anderostanediol and indomethacin on acquisition, consolidation and retrieval stage of spatial memory in adult male rats

BACKGROUND

Testosterone and its metabolites have important roles in learning and memory. The current study has conducted to assess the effect of pre-training, post-training and pre-probe trial intrahippocampal CA1 administration of 3α-anderostanediol (one of the metabolites of testosterone) and indomethacin (as 3α-hydroxysteroid dehydrogenase enzyme blocker) on acquisition, consolidation and retrieval in Morris water maze (MWM) task.

METHODS

Adult male rats were bilaterally cannulated into CA1 region of hippocampus and then received 3α-diol (0.2, 1, 3 and 6 mug/0.5 mul/side), indomethacin (1.5, 3 and 6 mug/0.5 mul/side), indomethacin (3 mug/0.5 mul/side) + 3α-diol (1 mug/0.5 mul/side), 25-35 min before training, immediately after training and 25-35 min before probe trial in MWM task.

RESULTS

Our results showed that injection of 3α-diol and indomethacin significantly increased the escape latency and traveled distance to find hidden platform in acquisition and consolidation stage, but did not have any effect on retrieval of spatial learning as compared with the control group.

CONCLUSION

It is concluded that intra-CA1 administration of 3α-diol and indomethacin could impair spatial learning and memory in acquisition and consolidation stage. Also, intrahippocampal injection of indomethacin + 3α-diol could not change spatial learning and memory impairment effect of indomethacin or 3α-diol in MWM task.

Testosterone regulation of Alzheimer-like neuropathology in male 3xTg-AD mice involves both estrogen and androgen pathways

Normal, age-related depletion of the androgen testosterone is a risk factor for Alzheimer's disease (AD) in men. Previously, we reported that experimental androgen depletion significantly accelerates development of AD-like neuropathology in the 3xTg-AD triple-transgenic mouse model of AD, an effect prevented by androgen treatment. Because testosterone is metabolized in brain into both the androgen dihydrotestosterone (DHT) and the estrogen 17β-estradiol (E2), testosterone can mediate its effects through androgen and or estrogen pathways. To define the role of androgen and estrogen pathways in regulation of AD-like neuropathology, we compared the effects of testosterone (T) and its metabolites DHT and E2 in male 3xTg-AD mice depleted of endogenous sex steroid hormones by gonadectomy (GDX). Male 3xTg-AD mice were sham GDX or GDX, immediately treated with vehicle, T, DHT, or E2, and 4 months later evaluated for two indices of AD-like neuropathology, β-amyloid (Aβ) accumulation and tau hyperphosphorylation. In comparison to sham GDX mice, we observed a significant increase in Aβ accumulation in GDX mice in subiculum, hippocampus, and amygdala. Treatment of GDX mice with T prevented the increased Aβ accumulation in all three brain regions. DHT treatment yielded similar results, significantly reducing Aβ accumulation across brain regions. Interestingly, E2 prevented Aβ accumulation in hippocampus but exerted only partial effects in subiculum and amygdala. Levels of tau hyperphosphorylation in sham GDX male 3xTg-AD mice were modest and only slightly increased by GDX. Treatment of GDX mice with T or E2 but not DHT reduced tau hyperphosphorylation to levels lower than observed in sham animals. These data suggest that testosterone regulates Aβ pathology through androgen and estrogen pathways and reduces tau pathology largely through estrogen pathways. These findings further define hormone pathways involved in regulation of AD-related pathology, information that is important for understanding disease etiology and developing pathway-specific hormone interventions.

3alpha-androstanediol, but not testosterone, attenuates age-related decrements in cognitive, anxiety, and depressive behavior of male rats

Some hippocampally-influenced affective and/or cognitive processes decline with aging. The role of androgens in this process is of interest. Testosterone (T) is aromatized to estrogen, and reduced to dihydrotestosterone (DHT), which is converted to 5α-androstane, 3α, 17α-diol (3α-diol). To determine the extent to which some age-related decline in hippocampally-influenced behaviors may be due to androgens, we examined the effects of variation in androgen levels due to age, gonadectomy, and androgen replacement on cognitive (inhibitory avoidance, Morris water maze) and affective (defensive freezing, forced swim) behavior among young (4 months), middle-aged (13 months), and aged (24 months) male rats. Plasma and hippocampal levels of androgens were determined. In experiment 1, comparisons were made between 4-, 13-, and 24-month-old rats that were intact or gonadectomized (GDX) and administered a T-filled or empty silastic capsule. There was age-related decline in performance of the inhibitory avoidance, water maze, defensive freezing, and forced swim tasks, and hippocampal 3α-diol levels. Chronic, long-term (1–4 weeks) T-replacement reversed the effects of GDX in 4- and 13-month-old, but not 24-month-old, rats in the inhibitory avoidance task. Experiments 2 and 3 assessed whether acute subcutaneous T or 3α-diol, respectively, could reverse age-associated decline in performance. 3α-diol, but not T, compared to vehicle, improved performance in the inhibitory avoidance, water maze, forced swim, and defensive freezing tasks, irrespective of age. Thus, age is associated with a decrease in 3α-diol production and 3α-diol administration reinstates cognitive and affective performance of aged male rats.

Testosterone and dihydrotestosterone differentially improve cognition in aged female mice

Compared with age-matched male mice, female mice experience a more severe age-related cognitive decline (ACD). Since androgens are less abundant in aged female mice compared with aged male mice, androgen supplementation may enhance cognition in aged female mice. To test this, we assessed behavioral performance on a variety of tasks in 22- to 24-mo-old gonadally intact female mice treated for 6 wk with silastic capsules containing either testosterone (T) or dihydrotestosterone (DHT) or empty capsules (placebo). Compared with placebo-treated mice, spatial memory retention in the water maze was enhanced by testosterone treatment, but not DHT treatment. In contrast, DHT treatment improved passive avoidance (PA) retention, while T treatment only did so marginally. These data support that androgen supplementation in old female mice improves cognitive performance differentially depending upon the type of hormone treatment and cognitive task.

Gonadal hormones modulate sex differences in judgments of relative numerousness in meadow voles, Microtus pennsylvanicus

Animals in a variety of taxa discriminate between a greater quantity and a lesser quantity of the same object, an ability that is referred to as relative numerousness judgment. For example, meadow voles can distinguish between areas containing more over-marks by one opposite-sex scent donor and fewer over-marks by another opposite-sex scent donor. Females appear to be able to make better discriminations between more or less over-marks than do males. In that gonadal hormones have been implicated in modulating cognitive function associated with spatial tasks, we tested the hypothesis that high titers of testosterone and estradiol are necessary for male and female voles, respectively, to distinguish between the top- and bottom-scent donors in an area containing mixed over-marks. We gonadectomized voles, giving them either gonadal hormone replacement (testosterone for males and estradiol for females) or no hormone replacement, and tested their spontaneous judgments of distinguishing between the top- and bottom-scent donors in an area containing mixed over-marks; a task involving judgments of relative numerousness. Female voles given replacement estradiol performed better than did female voles not given replacement estradiol in determining the top-scent and bottom-scent males in areas containing mixed over-marks. In contrast, males not treated with replacement testosterone performed better than did males treated with testosterone in determining the top-scent and bottom-scent males in areas containing mixed over-marks. Thus, high titers of estradiol and low titers of testosterone are associated with better performance on tasks involving relative numerousness in female and male voles, respectively. The results of this task on relative numerousness judgments are discussed in relation to the effects of gonadal steroid hormone on spatial ability, a closely related cognitive domain, and the social biology of meadow voles.

Region and sex differences in constituent dopamine neurons and immunoreactivity for intracellular estrogen and androgen receptors in mesocortical projections in rats

Many cortical and prefrontal functions show sex differences in their development, adult capacity, and dysfunction in disorders like schizophrenia. Correlations between circulating gonadal hormones and certain prefrontal functions have also been identified in humans and experimental animal models. Although multiple mechanisms may be involved, such hormone sensitivities/sex differences could be related to gonadal steroid actions on another regulator of cortical/prefrontal cortical function, the mesocortical dopamine system. Thus, although it is well known that perturbations in prefrontal dopamine signaling induce behavioral deficits, it is also known that several endpoints of these afferents are sensitive to gonadal steroids and/or are sexually dimorphic. This study explored possible substrates for this in two ways: by comparing the distributions of immunoreactivity for intracellular estrogen (alpha and beta) and androgen receptors among retrogradely labeled dopaminergic and nondopaminergic mesocortical neurons projecting to prefrontal, premotor, and primary motor cortices, areas in which male rat dopamine axons are differentially hormone-sensitive; and by comparing anatomical data in males and females. These analyses revealed region-, cell-, and sex-specific specializations in receptor localization that paralleled established patterns of mesocortical hormone sensitivity, including the androgen sensitivity of dopamine axons and dopamine-dependent functions in prefrontal cortex. It was also found that the proportions of dopamine neurons making up mesocortical projections were approximately 30% in males, whereas in females, significantly more constituent cells were dopaminergic. Together, these features may be part of the neurobiology giving mesocortical afferents their hormone sensitivities and/or sex differences in physiology, function, and dysfunction in disease.

Cognitive effects of hormone therapy in men with prostate cancer: a review

BACKGROUND

Men who receive androgen-deprivation therapy (ADT) for prostate cancer experience several side effects from this treatment. A few recent studies have examined the cognitive implications of ADT and how they impact a patient's treatment decision-making, occupational pursuits, and quality of life. For this report, the authors explored possible mechanisms for this association, reviewed research in animal studies and aging men, and examined the growing literature focused on the relation between ADT and cognitive functioning in patients with prostate cancer.

METHODS

A systematic literature search was conducted using the PubMed and Information Sciences Institute Web of Knowledge-Web of Science databases to identify relevant studies that investigated the relation between ADT in men with prostate cancer and its cognitive effects.

RESULTS

Testosterone and its derivatives may have an impact on cognition through several mechanisms in the brain, as supported by studies of animals and in aging men. Studies that researched the impact of ADT on cognition in patients with prostate cancer patients were designed relatively well but suffered from small sample sizes. Between 47% and 69% of men on ADT declined in at least 1 cognitive area, most commonly in visuospatial abilities and executive functioning. Some studies reported contradictory results with increased functioning in verbal memory.

CONCLUSIONS

There is a strong argument that androgen-ablation therapy is linked to subtle but significant cognitive declines in men with prostate cancer. The authors believe that clinicians should become aware of this correlation as the use of ADT increases and should inform and monitor patients for this possible side effect of treatment.

Influence of sex steroid hormones on spatial memory in a songbird

In mammals, sex steroid hormones influence spatial learning and memory abilities but there are few data regarding such effects in birds. We investigated whether non-invasive sex steroid hormone treatment would affect spatial memory task performance of great tits (Parus major). For five consecutive days, birds were fed wax moth larvae injected with either 80 microg testosterone or 80 microg estradiol carried in peanut oil immediately prior to behavioral testing. During the 5 days prior to and the 5 days following hormone treatment, birds were fed vehicle-injected larvae. Both hormone manipulations resulted in an elevation of circulating hormone levels within 5 min of larva ingestion. This elevation was sustained for at least 30 min but had no short-term (<1 day) effect on spatial memory performance. However, performance tended to increase during the first 5 days of vehicle treatment and during both sex steroid treatments whereas it decreased during the 5 days of vehicle treatment following either hormone treatment. These results suggest that both hormones led to some improvement in spatial memory that declined once treatment ended. The great tit hippocampus was found to express androgen and estrogen receptors which would provide a direct site of sex steroid action.

Effects of gonadectomy and hormone replacement on a spontaneous novel object recognition task in adult male rats

Recent studies in adult male rats have shown that gonadal hormones influence performance on certain working memory and other types of cognitive tasks that are sensitive to lesions of the medial and/or orbital prefrontal cortices. This study asked whether gonadal hormone modulation of prefrontal cortical function in males also extends to the perirhinal division of the rat prefrontal cortex. Specifically, sham-operated control, gonadectomized, and gonadectomized rats supplemented with testosterone propionate or estradiol were tested on a spontaneous novel object recognition task, a paradigm where performance has been shown to be impaired by perirhinal cortical lesions. Using analyses of variance, regression analyses and post-hoc testing to evaluate group differences, it was found that during both the sample and test trials of the task all four groups spent similar absolute and proportional amounts of time ambulating, rearing, stationary, and exploring the two objects present. All groups also explored each of the two identical objects present during sample trials equally. However, during the test trials, only the control and gonadectomized rats given testosterone showed the expected increase in exploration of the novel objects presented, whereas the gonadectomized and gonadectomized, estradiol-supplemental groups continued to explore the novel and familiar objects equally. That regression analyses also identified significant correlations between low bulbospongiosus muscle weight and impaired novel vs. familiar object discrimination further indicates that gonadectomy in adult male rats adversely affects spontaneous novel object recognition in an androgen-sensitive, estrogen-insensitive manner.

Sex-specific effects of gonadectomy and hormone treatment on acquisition of a 12-arm radial maze task by Sprague Dawley rats

The effects of gonadectomy and hormone treatment on spatial learning were evaluated in adult male and female rats using a modified version of a 12-arm radial maze task. In this version, procedures were used to minimize the effectiveness of strategies less reliant on working and reference memory. Results demonstrate significant sex differences favoring male performance on the working memory component of the task. In contrast, females performed slightly better than males on the reference memory component of the task. In females, ovariectomy produced a decrease in overall accuracy (i.e. an increase in the number of arm entries necessary to obtain all food pellets) as well as declines in working and reference memory performance. Both accuracy and working memory performance, but not reference memory performance, were restored by estradiol treatment. In males, castration impaired working memory performance but did not significantly affect overall accuracy or reference memory performance. Surprisingly, all groups of males performed poorly on the reference memory component of the task, and testosterone treatment appeared to worsen, rather than improve, both accuracy and reference memory performance in males. This may reflect a male preference for certain strategies that were rendered ineffective on this task. Significant sex differences, as well as treatment effects, on arm preference patterns were also detected; however, these differences were not sufficient to account for the effects of sex and treatment on acquisition. Collectively, the data demonstrate robust effects of gonadectomy and hormone treatment on acquisition of this modified radial arm maze task in females, with lesser effects in males.

Classical androgen receptors in non-classical sites in the brain

Androgen receptors are expressed in many different neuronal populations in the central nervous system where they often act as transcription factors in the cell nucleus. However, recent studies have detected androgen receptor immunoreactivity in neuronal and glial processes of the adult rat neocortex, hippocampal formation, and amygdala as well as in the telencephalon of eastern fence and green anole lizards. This review discusses previously published findings on extranuclear androgen receptors, as well as new experimental results that begin to establish a possible functional role for androgen receptors in axons within cortical regions. Electron microscopic studies have revealed that androgen receptor immunoreactive processes in the rat brain correspond to axons, dendrites and glial processes. New results show that lesions of the dorsal CA1 region by local administration of ibotenic acid reduce the density of androgen receptor immunoreactive axons in the cerebral cortex and the amygdala, suggesting that these axons may originate in the hippocampus. Androgen receptor immunoreactivity in axons is also decreased by the intracerebroventricular administration of colchicine, suggesting that androgen receptor protein is transported from the perikaryon to the axons by fast axonal transport. Androgen receptors in axons located in the cerebral cortex and amygdala and originating in the hippocampus may play an important role in the rapid behavioral effects of androgens.

Androgen administration to aged male mice increases anti-anxiety behavior and enhances cognitive performance

Although androgen secretion is reduced with aging, and may underlie decrements in cognitive and affective performance, the effects and mechanisms of androgens to mediate these behaviors are not well understood. Testosterone (T), the primary male androgen, is aromatized to estrogen (E(2)), and reduced to dihydrotestosterone (DHT), which is converted to 5alpha-androstane, 3alpha, 17beta-diol (3alpha-diol). To ascertain whether actions of the neuroactive metabolite of T, 3alpha-diol, mediates cognitive and affective behaviors, intact, aged male C57/B6 mice (24 month old) as well as young, intact and gonadectomized (GDX; 12 week old) mice were administered s.c. T, 3alpha-diol, E(2), or sesame oil vehicle (1 mg/kg; n=4-5/group) at weekly intervals and 1 h later mice were tested in the activity box, roto-rod, open field, elevated plus maze, zero maze, mirror maze, dark-light transition, forced swim, or Vogel tasks. Mice were trained in the inhibitory avoidance or conditioned contextual fear and were administered hormones following training and then were tested. After the last test occasion, tissues were collected for evaluation of hormone levels and effects on gamma-aminobutyric acid (GABA)-stimulated chloride flux. T, 3alpha-diol, or E(2) increased anti-anxiety and antidepressant behavior of aged, intact mice in the open field, light-dark transition, mirror maze, and forced swim tasks. T or 3alpha-diol, but not E(2), enhanced anti-anxiety behavior in the elevated plus maze, zero maze, and the Vogel task, and increased motor behavior in the activity monitor, latency to fall in the Roto-rod task, and cognitive performance in the hippocampally-mediated, but not the amygdala-mediated, portion of the conditioned fear task and in the inhibitory avoidance task. Anti-anxiety and enhanced cognitive performance was associated with regimen that increased plasma and hippocampal 3alpha-diol levels and GABA-stimulated chloride flux. Similar patterns were seen among young, adult GDX but not in intact mice. Thus, 3alpha-diol can enhance affective and cognitive behavior of male mice.

Cognitive impairment and increased brain neurosteroids in adult rats perinatally exposed to low millimolar blood alcohol concentrations

Epidemiological evidence suggests that adolescents and adults perinatally exposed to alcohol, even at low doses, show high prevalence of cognitive impairment and social behavior deficits, which may be in part related to alcohol-induced changes of the gamma-aminobutyric acid (GABA)ergic neurotransmission. The endogenous neurosteroid 3alpha-hydroxy,5alpha-pregnan-20-one (3alpha,5alpha-tetrahydroprogesterone/3alpha,5alpha-THP), a potent positive allosteric modulator of GABA(A) receptor function, is implicated in the physiological tuning of GABA-mediated fast inhibition and in various alcohol's actions in the brain. This study was undertaken to determine whether perinatal exposure to low millimolar blood alcohol concentrations alters cognitive skills (social discrimination and inhibitory avoidance tests), emotional reactivity (elevated plus maze test), and neurosteroid content in brain cortex and hippocampus of adult male offspring. Dams had access to a 3% alcohol solution or to an equicaloric sucrose solution from gestational day 15 to postnatal day 9. Eighty-day old alcohol-exposed male offspring exhibited impaired social recognition memory, but unchanged inhibitory avoidance performance and normal behavior on the elevated-plus maze. The concentrations of 3alpha,5alpha-THP and its precursor progesterone were more than doubled in brain cortex and hippocampus of alcohol-exposed rats, whereas in plasma only progesterone was increased. Thus, exposure to low millimolar blood alcohol concentrations has a long-lasting impact on the developing brain as it causes an impairment of social recognition as well as an increase of brain neurosteroid content in mature animals. The latter may be consequent to altered expression/activity of brain steroidogenic enzymes, as reflected by the enduring increase of the GABA(A) receptor-active neurosteroid 3alpha,5alpha-THP in brain cortex and hippocampus, but not in plasma. It is speculated that, by inducing a greater amplification of GABA(A) receptor function, the elevation of 3alpha,5alpha-THP brain content contributes to the cognitive impairment exhibited by adult alcohol-exposed offspring.

Activation of the androgen receptor alters the intracellular calcium response to glutamate in primary hippocampal neurons and modulates sarco/endoplasmic reticulum calcium ATPase 2 transcription

Androgens have been shown to have a number of effects on hippocampal function. Although androgen receptors (AR) are found at high levels in hippocampal neurons, the intracellular mechanisms responsible for androgen's actions are unknown. If androgens were capable of altering internal calcium concentration ([Ca(2+)](i)), they could influence a variety of intracellular signaling pathways, maintain neuronal homeostasis and Ca(2+) induced excitotoxicity. In the present study, calcium imaging was used to measure the [Ca(2+)](i) in rat primary hippocampal neurons treated with either the AR agonist dihydrotestosterone (DHT), DHT+flutamide (AR antagonist), flutamide alone, or vehicle for 24 h and subsequently presented with an excitatory glutamate stimulus. In the absence of glutamate stimulation, DHT treatment caused a significant upward shift in baseline [Ca(2+)](i) when compared with neurons from all other groups. Glutamate had a greater effect on [Ca(2+)](i) in DHT-treated neurons and DHT-treated neurons returned to baseline levels significantly faster than all other groups. Cyclopiazonic acid, an inhibitor of sarco/endoplasmic reticulum calcium ATPase (SERCA) had a larger response in DHT-treated neurons compared with controls, suggesting increased Ca(2+) stores in DHT-treated neurons. In all cases the effects of DHT were blocked by treatment with flutamide indicating an AR-mediated mechanism. To determine a possible mechanism by which AR activation could be influencing [Ca(2+)](i), SERCA2 mRNA levels were measured in primary hippocampal neurons. SERCA2 is inserted into the endoplasmic reticulum (ER) membrane and functions to rapidly pump [Ca(2+)](i) into the ER. Following treatment of primary hippocampal neurons with DHT, SERCA2 mRNA was increased, an effect that was blocked in the presence of flutamide. Taken together these results indicate that DHT, working through AR, causes an up-regulation of SERCA2, which increases the sequestering of [Ca(2+)](i) in the endoplasmic reticulum of hippocampal neurons. Such changes may allow the neurons to respond more robustly to a stimulus and recover more quickly following a highly stimulatory challenge.